OpenWrt One - celebrating 20 years of OpenWrt

[Piotr Dymacz]

Hi Chuanhong,

On 9.01.2024 14:51, Chuanhong Guo wrote:
> Hi!
> 
> On Tue, Jan 9, 2024 at 6:52 PM John Crispin <john at phrozen.org> wrote:
>> [...]
>> FAQ
>>
>> * Why are there are 2 different flash chips?
>> - the idea is to make the device (almost!) unbrickable and very easy to
>> recover
> 
> What about a built-in JTAG probe instead of SPI-NOR+USB-UART?
> It'll be actually unbrickable instead.

We were considering similar idea but that would involve additional 
testing and extra work on the manufacturer's side procedures 
(programming and testing the MCU). I believe avoiding this would speed 
up things and getting the device made.

The dual-flash solution with a mechanical switch seems as simple as 
possible in terms of required user's actions for unbricking the device 
and at the same time, doesn't force user to use specific tools and/or OS.

Experienced users could still use the regular JTAG connector on-board.

>> - NAND will hold the main loader (U-Boot) and the Linux image and will
>> be the default boot device
>> - NOR will be write-protected by default (with WP jumper available on
>> the board) and will hold a recovery bootloader (and other essential
>> data, like Wi-Fi calibration)
>> - a dedicated boot select switch will allow changing between NOR and NAND
>> [...]
>> * What is the purpose of the console USB-C port?
>> - Holtek UART to USB bridge with CDC-ACM support on USB-C makes the
>> device ultra easy to communicate with. No extra hardware or drivers will
>> be required. Android for example has CDC-ACM support enabled by default
> 
> There are several MCU-based CMSIS-DAP projects out there. They can
> provide a CDC-ACM serial with a JTAG interface. It may be a bit slow if a
> USB1.1 MCU is picked, but it should be enough to start a bootloader to
> unbrick the device.
> 
> Here's one with USB2.0 Hi-speed interface:
> https://github.com/cherry-embedded/CherryDAP
> The Sipeed M0S module used costs 20CNY on Taobao
> (or 2.81 USD according to google)

I like the idea, could be probably combined with some of the suggestions 
from Bjørn. But at least for now, let's KISS and keep these ideas for 
future, maybe.

-- 
Cheers,
Piotr